When a power supply system is constructed, in addition to a further expansion of a power distribution grid in a more stable way, a main issue has been providing such a system with a capability of introducing a large amount of natural energy. A power network system called Digital Grid (registered trademark) has been proposed as a new power network (see Patent literatures 1 and 2.
Digital Grid (registered trademark) is a power network system in which a power network is partitioned into small-sized cells and these cells are asynchronously interconnected. Each power cell may be small (e.g., a house, a building, or a commercial facility) or may be large (e.g., a prefecture or a municipality). Each power cell naturally includes a load, and may also include a power generation facility or a power storage system. The power generation facility may be, as an example, a power generation facility that uses natural energy generated by, for example, photovoltaic power, wind power, and geothermal power.
In order to freely generate power inside each power cell and to further smoothly interchange power among the power cells, the power cells are asynchronously connected. That is, even when the plurality of power cells are interconnected, a frequency, a phase, and a voltage of power used in each power cell is asynchronous with those used in other power cells.
FIG. 15 shows an example of a power network system 810. In FIG. 12, a utility grid 811 sends bulk power from a large-scale power plant 812. A plurality of power cells 821-824 are arranged. Each of the power cells 821-824 includes a load such as a house 831 and a building 832, power generation facilities (e.g., a solar panel 833 and an wind turbine 834), and a power storage system (e.g., a storage battery 835).
In the specification of the present application, power generation facilities and power storage systems are also collectively referred to as “distributed power supplies”.
Further, the power cells 821-824 respectively include power routers 841-844 which serve as connection ports to be connected to other power cells or the utility grid 811. Each of the power routers 841-844 includes a plurality of legs (LEG). (Due to space constraints, the symbols for the legs are omitted in FIG. 15. It should be interpreted that the white circles attached to the power routers 841-844 are connection terminals of each leg.)
Now, each leg includes a connection terminal and a power conversion unit, and an address is attached to each leg. The power conversion by the leg means converting AC to DC or DC to AC and changing the phase, the frequency, and the voltage of the power.
All the power routers 841-844 are connected to a management server 850 by a communication network 851, and operations of all the power routers 841-844 are integrally controlled by the management server 850. For example, the management server 850 instructs each of the power routers 841-844 to transmit or receive power for each leg. Accordingly, power is interchanged among power cells through the power routers 841-844.
Since power interchange among the power cells is achieved, a plurality of power cells can share, for example, one power generation facility (e.g., the solar panel 833 and the wind turbine 834) or one power storage system (the storage battery 835). If an excessive power can be interchanged among the power cells, a supply-demand balance of power can be kept stable while greatly reducing the equipment cost.